1. Technical Field of the Invention
The present invention relates to a method for forming a pattern by a droplet discharge system.
2. Description of the Related Art
An example of a conventional method for forming a wiring pattern by a droplet discharge system (hereinafter, referred to as an inkjet system) is a method described in Japanese Unexamined Patent Application Publication No. 2002-164635. According to the method disclosed herein, in order to form an accurate wiring pattern, a lyophilic section and a liquid repellent section are formed into a specified pattern on a substrate surface with an organic molecule layer, thereby selectively dropping a liquid containing electrically conductive ultra-fine particles onto the lyophilic section.
The wiring-pattern forming technique by the inkjet system is required to reduce the width of the wire. To this end, the applicant has proposed a method for forming small droplets by dropping the liquid on a substrate surface processed to be liquid repellent (for example, refer to Japanese Patent Application No. 2002-089810, unpublished at the present time).
An example of the method for making a liquid-repellent substrate surface is a method of forming a self-assembled layer on the substrate surface with, for example, fluoroalkylsilane. The fluoroalkyl group is thus disposed on the surface of the self-assembled layer to make the substrate surface liquid repellent.
Specifically, for example, 10-g of hexadecafluoro-1,1,2,2-tetrahydrodecyltriethoxysilane and a glass substrate are held at 120° C. for two hours in a 10-liter airtight container.
According to this method, however, when a liquid is dropped on the liquid-repellent substrate, droplets each having a small contact angle with respect to the substrate are formed. Also, to form a layer containing electrically conductive ultra-fine particles in sufficient grain density, it is necessary to closely dispose a large number of droplets. Accordingly, the large number of droplets are connected to form a large amount of solvent on the substrate, increasing the droplet width on the substrate. Thus, the wiring width tends to become larger than a set value.
Since the droplets are formed on the liquid-repellent substrate, the adhesion of the wiring layer (a layer containing electrically conductive ultra-fine particles) becomes disadvantageously low. Furthermore, this has the problem of taking much labor to make the substrate surface water repellent.
As a method for preventing the expansion of the wiring width, it has been proposed to provide a receptor layer on the substrate surface for absorbing the solvent, for example, refer to Japanese Unexamined Patent Application Publication No. 05-50741. The method of absorbing the solvent by providing a porous membrane as the receptor layer is susceptible to improvement in the adhesion of the wiring layer.
Japanese Unexamined Patent Application Publication No. 2002-324966 describes a method for drawing a circuit pattern on a wiring substrate with electrically conductive metal paste by an inkjet system.
It, however, is also difficult to form a wire having a thin width with high adhesion to the substrate using this method.